This invention relates to electromechanical transducers and, more particularly, to a transducer configuration employing a number of separate transducers for monitoring a plurality of different pressure sensitive areas.
Pressure transducers employing semiconductor devices as piezoresistors are in wide-spread use and serve to measure force or pressure in a number of different environments.
One particular application is the use of such devices for measuring pressures or forces exerted on a model placed in a wind tunnel to define flow phenomenon. As such, the ultra-minature transducers or those employing piezoresistive bridge configurations, mounted on silicon diaphragms of between 0.25 to 0.03 inches or less, have received widespread use in wind tunnel applications for measuring pressure fluctuations in the local outside area of inlet/engine subsystems.
There are many considerations employed in the design and fabrication of transducers for such environments and a good review of such requirements may be had by referring to a publication entitled NOTES ON APPLICATIONS OF INTEGRATED SENSOR (IS) PRESSURE TRANSDUCER, Published by Kulite Semiconductor Products, Inc. as Application Note KPS-AN11. This publication contains a series of articles depicting and defining transducer requirements for wind tunnel tests and the like.
In any event, a wind tunnel or similar test on an engine, or an airplane part requires the measuring and monitoring of pressure at a relatively large number of points about and along the test object.
The prior art utilized many approaches to accomplish this. Separate transducers for each point could be employed, but present a problem in regard to calibration of each device, offset differences between each transducer due to manufacturing techniques and so on.
Another widely used approach was employing one or more high quality transducer assemblies and using the single assembly to monitor a plurality of points by mechanically switching a plurality of pressure tubes coupled between the transducer and each point to be monitored.
This system employed mechanical scanners, valves to close or open the pressure ports and so on. The mechanical switching assemblies and the valves experience high failure rate and are difficult and expensive to maintain.
Furthermore, the rate of mechanical scanning is substantially limited due to mechanical operation as well as the necessity of allowing the transducer to equalize each time a new pressure point is accessed. For example, if one high quality transducer is switched between varying pressure points, it is possible that the point may be at a pressure of 100 psi and the next succeeding point may be at a pressure of 10 psi or ten times less.
The transducer employs a moving diaphragm, has hysteresis and the system has inertia. Hence, if the scanning rate is fast, the output will be incorrect since the reading of the transducer will be determined by the previous pressure.
It is therefore an object of the present invention to provide a multiple pressure transducer configuration having the capability of monitoring a plurality of pressure points by a plurality of individual transducers, fabricated by similar techniques and mounted in a common housing, thus subjecting all the transducers to a similar environment.